Firstly... congratulations on both offers 'tryingtobesmart'
I'm just going to give a JMSS perspective (since no-one has LOL) but really it is a great school and I'm glad I didn't accept my offer when I got into MHS (so I was in the same situation as you but just being a guy LOL)
Before anything happens... have you considered: Travel time, prestige(?) and subject opportunities?
Elaborating on the latter, JMSS has little subject opportunities in terms of the Humanities department (E.g No Legal Studies, Business Management). We do offer subjects catering for Humanities but not a lot really....
As 'teletubbies_95' has stated:
the girls you meet are so amazing and dedicated to watever they do
is true however you are heading into Year 10 where people have formed social groups already from Year 9 onwards. It'll take time fitting in (not saying you won't) but at JMSS everyone is all new and you'll bond really quick as a cohort at camp and at school because everyone is new and ready to 'fit in.' Talking about nerdy stuff is perfectly fine (science pick-lines (Y) ) and most of us share the same interest in you (being Maths and Science).
JMSS offers pretty amazing opportunities in the field of science and ones that aren't necessarily offered at Mac.Rob. Although Mac.Rob offers programs which JMSS don't cater for, we are a science school and we cater for that particular field. Such things include
Supercomputing Conference,
International Science Fairs and
International Student Science Fairs (which JMSS hosts in 2015 which you'll be here for [hopefully]) and many more.
JMSS is located at Monash University (Clayton) and we go over to the university to do stuff and pretty soon you'll be accustomed to the campus itself and get a little taste of 'uni life' (not saying all but the you get to soak up the feel of it etc.). We leech off Monash Uni's Internet so it's pretty quick too (free wifi on your smartphones or whatever too)
Not really necessary but we have boys...

(not that it'll have an influence on your decision but some of them are pretty......)
I'll have to agree and say some of the teachers aren't that great (but some are amazing).
I have 2 students from JMSS - their teachers often test them on things which are not on the course. I would go to mac.rob (if i were a girl...)
Depending on year level but if it's Year 10 then wouldn't really matter because it's Year 10 and not VCE (however if it's in Year 11-12 then it could possibly but I wouldn't have a clue being in Year 10

)
There are things that could be improved on as well (E.g Co-curricular activities) but overall the environment at JMSS is pretty good and personally I enjoy being at JMSS.
Good luck on your decision and if you need to ask any more questions then feel free to PM me
